* Ram Pai: > On Thu, Nov 08, 2018 at 01:05:09PM +0100, Florian Weimer wrote: >> Would it be possible to reserve a bit for PKEY_DISABLE_READ? >> >> I think the POWER implementation can disable read access at the hardware >> level, but not write access, and that cannot be expressed with the >> current PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE bits. > > POWER hardware can disable-read and can **also disable-write** > at the hardware level. It can disable-execute aswell at the > hardware level. For example if the key bits for a given key in the AMR > register is > 0b01 it is read-disable > 0b10 it is write-disable > > To support access-disable, we make the key value 0b11. > > So in case if you want to know if the key is read-disable 'bitwise-and' it > against 0x1. i.e (x & 0x1) Not sure if we covered that alreay, but my problem is that I cannot translate a 0b01 mask to a PKEY_DISABLE_* flag combination with the current flags. 0b10 and 0b11 are fine. POWER also loses the distinction between PKEY_DISABLE_ACCESS and PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE, but that's fine. This breaks the current glibc test case, but I have a patch for that. Arguably, the test is wrong or at least overly strict in what it accepts. Thanks, Florian
